1. Field of the Invention
The present invention relates in general to a method of removing a diamond coating from a diamond-coated body, and a method of manufacturing a diamond-coated body by reutilizing a substrate from which the diamond coating has been removed.
2. Discussion of the Related Art
There is known a diamond-coated body, such as a cutting tool (e.g., an end mill, a throwaway or disposable insert) and a semiconductor device (e.g., a semiconductor laser, a semiconductor sensor), having a surface which is coated with a diamond coating in the interest of increasing a degree of wear resistance and a degree of surface hardness of the body, as disclosed in JP-B2-59-27753 and JP-B2-2519037. As a method of coating a substrate with a diamond coating, there are proposed various methods such as a microwave plasma CVD (chemical vapor deposition) method, a high-frequency plasma CVD method and an ion beam method.
Where the diamond coating of the diamond-coated body has been worn or damaged as a result of its long service, or where the body is defective due to unsatisfactory formation of the diamond coating in its manufacturing process, it is considered possible to grind the diamond coating so as to remove the diamond coating from the diamond-coated body, so that a substrate of the coated body is reutilized rather than discarded. However, the diamond coating is hard to be ground due to a high degree of hardness thereof, and is accordingly difficult to be removed from the substrate. Consequently, the removal of the diamond coating from the substrate is difficult and time-consuming, even giving rise to a risk of damaging or scratching the substrate of the diamond-coated body.
It is therefore a first object of the present invention to provide a method of efficiently removing a diamond coating from a substrate of a diamond-coated body in a short time without damaging or scratching the substrate.
It is a second object of the present invention to provide a method of manufacturing a diamond-coated body by reutilizing a substrate from which a diamond coating has been removed.
The first object may be achieved according to a first aspect of this invention, which provides a method of removing a diamond coating from a substrate of a diamond-coated body which includes the substrate coated with the diamond coating, the method comprising a step of heating the diamond-coated body at a predetermined temperature in a furnace or reactor at a predetermined reduced pressure, while introducing an oxygen gas into the reactor at a predetermined flow rate, for burning the diamond coating to thereby remove the diamond coating from the substrate.
According to the present method, the diamond-coated body is heated in the reactor at the predetermined reduced pressure or negative pressure while the oxygen gas is introduced at the predetermined flow rate, so that the diamond coating is burned by the introduced oxygen gas. This method permits the diamond coating to be removed from the substrate without damaging the substrate, more reliably in a shorter time than where the diamond coating is removed by grinding the diamond coating.
According to a first preferred form of the first aspect of the invention, the method further comprises a step of energizing an electromagnetic coil disposed in an outer peripheral portion of the reactor for thereby magnetizing the electromagnetic coil, while the diamond coating is burnt. In this method, the electromagnetic coil disposed in the outer peripheral portion of the reactor is energized or magnetized, so that the oxygen gas is activated owing to an electromagnetic force generated by the energized electromagnetic coil. As a result of the activation of the oxygen gas, the diamond-coated body is bombarded or pressed by oxygen ions (ionized oxygen), so that the burning of the diamond coating is facilitated or accelerated whereby the diamond coating is more satisfactorily removed from the substrate in a further reduced time.
According to a second preferred form of the first aspect of the invention, the predetermined temperature ranges from 600xc2x0 C. to 1000xc2x0 C., and the predetermined reduced pressure is not higher than 3000 Pa, and wherein the flow rate ranges from 0.1 L/min to 0.5 L/min. In these ranges of the respective temperature, pressure value and flow rate, the diamond coating is more satisfactorily burned, particularly, where the substrate made of a cemented carbide has been coated with the diamond coating, by using a microwave plasma CVD device. It is more preferable that the predetermined temperature is about 800xc2x0 C., namely, ranging from 750xc2x0 C. to 850xc2x0 C., that the predetermined reduced pressure is not higher than 1000 Pa, and that the flow rate is about 0.2 L/min, namely, ranging from 0.15 L/min to 0.25 L/min. It is to be understood that there is not a particular lower limit of the reduced pressure value in the reactor although the lower limit is preferably close to the absolute vacuum. For example, the lower limit may be determined depending upon the capacity of the used device, in such a range that the lower limit is not higher than about 100 Pa. It is also to be understood that the above-described temperature is interpreted to be a temperature at a surface of the diamond coating when the diamond coating is burnt, which temperature is measured by a radiation thermometer (emission thermometer).
According to a third preferred form of the first aspect of the invention, the reactor is provided by a microwave plasma CVD device, namely, the reactor consists of a reactor of the microwave plasma CVD device, so that the diamond-coated body is heated by a microwave. In this method, the diamond-coated body is heated by using the reactor of the microwave plasma CVD device which has been conventionally used in an operation for coating a substrate with a diamond coating. Thus, the diamond coating is more easily removed from the substrate at a further reduced cost, by utilizing such a conventional device.
The above-described second object may be achieved according to a second aspect of this invention, which provides a method of manufacturing a new diamond-coated body, by reutilizing a substrate of a diamond-coated body which includes the substrate coated with a diamond coating, the method comprising: (a) a removing step of removing the diamond coating from the substrate of the diamond-coated body, by burning the diamond coating; and (b) a coating step of coating a surface of the substrate, with a new diamond coating, for thereby obtaining the new diamond-coated body.
According to the present method, where the diamond coating of the diamond-coated body has been worn or damaged, or where the body is defective due to unsatisfactory formation of the diamond coating in its manufacturing process, the substrate of the diamond-coated body is recycled or reutilized, without newly preparing another substrate, for manufacturing a new diamond-coated body. That is, the substrate, from which the diamond coating has been burned out or removed, is recoated with a diamond coating, so as to produce the new diamond-coated body. The thus effective utilization of the existing substrate advantageously provides an increased yield ratio and a reduced manufacturing cost. The present method has another advantage that a desired diamond-coated body can be produced more efficiently than where the diamond-coated body is produced by using a newly prepared substrate. Further, by burning the diamond coating, the removal of the diamond coating can be completed without damaging the substrate, more reliably in a further reduced time, than where the diamond coating is removed by grinding. It is noted that the coating step may be interpreted as a recoating step of recoating the surface of the substrate with the diamond coating.
According to a first preferred form of the second aspect of the invention, the diamond coating is removed in accordance with the method defined in the first aspect of the invention. This method of the first preferred form of the second aspect provides the same advantageous effect as the above-described method of the first aspect of the invention.
According to a second preferred form of the second aspect of the invention, the desired diamond-coated body consists of a diamond-coated tool which has the substrate in the form of a tool substrate whose surface is coated with the diamond coating. This preferred form of the second aspect of the invention relates to a method of manufacturing the diamond-coated tool, in which the tool substrate is effectively utilized, resulting in a reduced cost for manufacturing the diamond-coated tool.
The diamond-coated tool may be, for example, an end mill or other cutting tool having a cutting edge formed on the tool substrate.
According to a third preferred form of the second aspect of the invention, the desired diamond-coated body consists of a diamond-coated semiconductor device which has the substrate in the form of a semiconductor device whose surface is coated with the diamond coating. This preferred form of the second aspect of the invention relates to a method of manufacturing the diamond-coated semiconductor device, in which the semiconductor device as the substrate is effectively utilized resulting in a reduced cost for manufacturing the diamond-coated semiconductor device.
The present invention is applicable to the diamond-coated tool, the diamond-coated semiconductor device or any other kind of diamond-coated bodies having respective substrates each of which does not have a risk of being damaged by the burning of the diamond coating.
In the practice of the method of the present invention, in which the diamond coating is burnt out by oxygen so as to be removed from the substrate, in general, burnt residues including impurities tend to remain sticking to the surface of the substrate, after the diamond coating has been burnt out by oxygen. In view of this tendency, the method may further include a step of wiping the surface of the substrate with a cloth containing fine abrasive grains, so as to remove the burnt residues from the surface. Particularly, in the practice of the method of the second aspect of the invention, in which the surface of the substrate is recoated with the diamond coating after the removal of the diamond coating from the substrate, it is preferable that the diamond coating is removed from the surface of the substrate as completely as possible.
In the method of the second preferred form of the first aspect of the invention, the temperature at which the diamond-coated body is heated ranges from 600xc2x0 C. to 1000xc2x0 C., the pressure value in the reactor is held not higher than 3000 Pa, and the flow rate at which the oxygen gas is introduced into the reactor ranges from 0.1 L/min to 0.5 L/min. However, the thus specified burning condition does not have to be necessarily applied to the removal of any kind of diamond-coated bodies, but may be suitably modified depending upon the coating method of the diamond coating, the material of the substrate and other factors.
Where the diamond coating is burnt in the burning condition specified in the second preferred form of the first aspect of the invention, the diamond coating can be burnt out in about 20-30 minutes. However, the burning time may be suitably changed depending upon, for example, the thickness of the diamond coating, the area of the diamond coating, and the number of the diamond-coated bodies which are simultaneously heated.
In the third preferred form of the first aspect of the invention, the microwave plasma CVD device is used so that the diamond-coated body is heated by the microwave. However, the used reactor may be any one of other devices which are designed for forming a diamond coating, or even any one of devices which are not designed for forming a diamond coating. Further, it is possible to employ a resistance heating or other heating method depending upon, for example, the material of the substrate, as long as the heating method makes it possible to raise the temperature at the surface of the diamond coating to about 600-1000xc2x0 C.
The coating step defined in the second aspect of the invention is preferably implemented with the microwave plasma CVD device in accordance with a microwave plasma CVD method. However, the coating step may be implemented in accordance with any other methods such as a high-frequency plasma CVD method and an ion beam method. Further, the method of the third preferred form of the first aspect of the invention in which the diamond-coated body is heated by the microwave in the microwave plasma CVD device can be applied not only where the substrate has been coated with the diamond coating in accordance with the microwave plasma CVD method but also where the substrate has been coated with the diamond coating in accordance with a method other than the microwave plasma CVD method.
The diamond-coated tool defined in the second preferred form of the second aspect of the invention may interpreted to mean an end mill, a drill, a tap, a threading die, a disposable or throwaway insert or other cutting tool having at least one cutting edge formed on its substrate, or a cold-forming tap, a cold-forming die or other cold-forming tool which is designed to form the workpiece into a desired shape by plastically deforming the workpiece. The tool substrate is preferably made of a cemented carbide, but may be made of a cermet, a ceramic or other material. Where the diamond-coated tool is coated with a new diamond coating after the removal of an old diamond coating, the cutting edge may be reground, as needed, so as to restore its original shape before the tool is coated with the new diamond coating.
The diamond-coated semiconductor device defined in the third preferred form of the second aspect of the invention may be interpreted to mean any one of various kinds of semiconductor sensors, semiconductor torsion gages, semiconductor storage elements, semiconductor switching elements, semiconductor lasers and other semiconductor devices each of which is provided by a semiconductor. As the semiconductor sensors, there are a photo sensor (e.g., a photodiode and a phototransistor) which utilizes a photo-electric effect, a displacement sensor which utilizes a magneto-resistance effect, a thermistor which utilizes a temperature dependency of an electric resistance, a pressure sensor which utilizes a piezo-electric effect, a magnetic sensor which utilizes the Hall effect, and a gas sensor which utilizes a variation in an electric resistance caused by a gas absorption.